The design of a seal, especially a dynamic seal with a rotating flexible seal body, involves several compromises. Such seal generally is located within a limited space between two relatively rotatable members, such as bearing races. This limits the possible size of the sealing body, especially the length thereof. Such a sealing body must have a certain thickness sufficient for the speeds involved to give it an inherent circumferential stability. Circumferential stability keeps the seal from rippling at high speed and keeps the seal in good sealing contact with a sealing surface. Since it is impractical to mold such a seal body directly to the rotating member, it is most conveniently molded to a separable casing which can be press fitted to one of the members. The press fit forces a lip of the seal body into secure sealing engagement with the sealing surface and deflects the seal body a certain amount. This deflection is resisted by the seal body in proportion to its thickness, which thickness is controlled by the other consideration discussed above. Therefore, the deflection necessary to give secure sealing engagement of the lip may in fact cause a higher frictional load of the lip on the sealing surface that would be ideally desirable.
In addition, the frictional load will increase at higher speeds of rotation. This problem is especially severe with seals of large diameter, required in applications where the seal is fitted over a member of large diameter, such as a large diameter constant velocity joint housing. An example of a seal in such an application may be seen in UK Pat. application No. GB 2,107,024-A.
The seal disclosed in the U.S. Pat. to Irwin No. 3,627,390 seeks to achieve adequate stationary sealing combined with reduced friction at high speeds by using the centrifugal force of rotation to lift the lip from its sealing surface. However, as may be seen FIG. 2 of the patent, this action is achieved by molding steel weights into the lip of the sealing body in order to get sufficient centrifugal force to move the lip away. Clearly, it would be desirable to eliminate these weights if possible, if this could be achieved within the limitations on seal body thickness and length discussed above.